The invention relates to joint packings or seals, but more particularly, the invention relates to flexible boots of the corrugated type for use with universal joints.
Flexible boots have long been used to protect the operating environment for universal joints by retaining grease for the joints and by keeping foreign objects away from the joints. The accomplishment of such functions over a suitable flex-life operating-period, while seemingly simple, is, in reality, more complex because damage to the boot must be avoided as much as possible to avoid early failures of the universal joint.
In use, damage to a flexible boot may be inflicted in several different ways such as for example by: a) external abrasion of corrugations caused by them rubbing against themselves as the boot is flexed and rotated with its ends in angular misalignment; b) internal abrasion of corrugations caused by the boot rubbing against part of an encased universal joint as the flexible boot is flexed and rotated with its ends in angular misalignment; and c) external abrasion and puncturing from external sources such as when the flexible boot is operated in a rocky or prodding environment. Additionally, the boot must have a requisite strength to inhibit ballooning when rotated while maintaining requisite flexibility and life over a broad temperature range and angle change.
Flexible boots may be categorized into two general groups based on an orientation of the corrugations in the flexible boot. In a first category, the corrugations are oriented generally radially, with peaks of the corrugations radially outward of valleys of the corrugations. Boot flexing is typically concentrated at the peaks and valleys and is in response to an induced force of an encased joint, the boot of a harder resilient material such as Hytrel as sold by Dupont and disclosed in the 4,747,805 patent, or a combination of two materials such as semirigid polymeric materials such as glass impregnated nylon as disclosed in the 4,627,826 patent. However, such solutions while inhibiting damage from external environmental sources such as by puncturing from rocks, etc. may introduce new problems including flex fatigue.
For example, the flexible boot of the '805 patent has a deflection problem like those boots having radially oriented corrugations in that the wall of the boot is pulled radially inwardly at the large diameter end of the boot and on the side of the boot that is flexed to an acute angle. The inward deflection of the boot sidewall may limit the number of degrees of deflection before the boot is pulled into interference with an encased universal joint.
As explained in the '826 patent, the axially oriented corrugations provide angular movements of up to 30 degrees but thereafter, a spherical member of the joint in conjunction with a socket portion of the boot are required and cooperate with each other to permit further angular movements of the boot. While the design of the '826 boot may permit sufficient angular movements, it requires a dynamic sealing arrangement between the spherical surface of the joint and a spherical socket of the boot. Such an arrangement is not only expensive but it is not 100 percent effective in forming a seal to retain grease. Also, constant sliding between the parts can cause wear leading to seal failure.
The present invention is primarily directed to flexible boots of the second category which have corrugations oriented generally axially in relation to the boot. The invention addresses general boot problems associated with self inflicted damage to corrugations, and damage associated with the boot contacting internal and external objects as the boot is angularly displaced to angles as high as 40 degrees.